Aerosol-generating systems with liquid level determination and methods of determining liquid level in aerosol-generating systems

ABSTRACT

An electrically operated aerosol-generating system may include a liquid storage portion configured to store a liquid from which aerosol may be generated, an electric heater, a capillary wick extending between the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater and electric circuitry connected to the electric heater. The electric circuitry may be configured to: activate the electric heater for a first heating time period in response to an input to vaporize liquid in the capillary wick, activate the electric heater for a second heating time period upon the elapse of a first cooling time period after the first heating time period, record a temperature measurement of the electric heater during the second heating time period, and determine an amount of liquid in the liquid storage portion based on the temperature measurement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority to,international application no. PCT/EP2017/050374, filed on Jan. 10, 2017,and further claims priority under 35 U.S.C. § 119 to European PatentApplication No. 16157420.7, filed Feb. 25, 2016, the entire contents ofeach of which are incorporated herein by reference.

BACKGROUND

Field

Some example embodiments relate to an electrically operatedaerosol-generating system. In particular, some example embodimentsrelate to an electrically operated aerosol-generating system in which anaerosol-forming substrate is liquid and is contained in a liquid storageportion.

Description of Related Art

WO 2012/085203 A1 discloses an electrically heated vaping system havinga liquid storage portion. The liquid storage portion includes a liquidaerosol-forming substrate and is connected to a vaporizer comprising anelectric heater which is powered by a battery supply. The electricheater is activated based on air being drawn through an outlet. Theheated aerosol-forming substrate contained in the vaporizer is vaporizedby the activated heater. Air drawn along or through the vaporizer basedon air being drawn through the outlet entrains and cools the vapor togenerate an aerosol. The generated aerosol is drawn through the outlet.An amount of depletion of liquid aerosol-forming substrate is determinedbased on a relationship between a power applied to the heating elementand a resulting temperature change of the heating element once theheating element is activated. The determined amount of depletion isindicated.

This approach relies on the fact that when there is less liquid in thevicinity of the heating element, for a given applied power, the heatingelement will be heated at a higher rate. So if the liquidaerosol-forming substrate is depleted to a level such that there is asignificant reduction in liquid in the vicinity of the heating elementwhen the heater is activated, then there will be a significantly highertemperature change of the heating element than under normal conditions,when the liquid storage portion is full of liquid. This means thatliquid depletion can only be determined when the level of liquid in theliquid storage portion has been significantly depleted. It also meansthat liquid level can only be determined as air is being drawn throughthe outlet.

It would be desirable to provide an aerosol-generating system thatdetermines the level of liquid in a liquid storage portion moreaccurately, particularly at times when the liquid storage portion is notnearly empty.

SUMMARY

According to some example embodiments, an electrically operatedaerosol-generating system may include a liquid storage portionconfigured to store a liquid from which aerosol may be generated, anelectric heater, a capillary wick extending between the liquid storageportion and the electric heater, and electric circuitry connected to theelectric heater. The capillary wick may be configured to convey liquidfrom the liquid storage portion to the electric heater. The electriccircuitry may be configured to activate the electric heater for a firstheating time period in response to an input to vaporize liquid in thecapillary wick, activate the electric heater for a second heating timeperiod upon an elapse of a first cooling time period after the firstheating time period, record a temperature measurement of the electricheater during or immediately following the second heating time period,and determine an amount of liquid in the liquid storage portion based onthe temperature measurement.

The first cooling time period may be shorter than a time periodassociated with an amount of liquid in the wick reaching equilibriumfollowing the first heating time period.

The electric circuitry may be configured to activate the electricheater, such that a temperature of the electric heater is lower than avaporization temperature of the liquid during the second heating timeperiod.

The electric circuitry may be configured to activate the electric heaterfor a third heating time period upon an elapse of a second cooling timeperiod after the second heating time period, record a temperaturemeasurement of the electric heater during the third heating time period,and determine an amount of liquid in the liquid storage portion based ona combination of the temperature measurement of the electric heaterduring the third heating time period and the temperature measurement ofthe electric heater during the second heating time period.

The electric circuitry may be configured to activate the electricheater, such that a temperature of the electric heater is lower than avaporization temperature of the liquid during the third heating timeperiod.

A sum of the first cooling time period, the first heating time periodand the second cooling time period may be shorter than a period ofelapsed time associated with an amount of liquid in the wick reachingequilibrium following the first heating time period.

The capillary wick may have a fibrous or spongy structure.

The liquid storage portion may be configured to retain the liquid in aliquid carrier material.

The second heating time period may be between 0.05 and 0.5 seconds.

The first cooling time period may be between 0.2 and 2 seconds.

The electric circuitry may include a memory. The memory may beconfigured to store a look-up table relating temperature measurements toliquid levels.

The electric circuitry may be configured to determine whether tosubsequently activate the electric heater for the second heating timeperiod upon the elapse of the first cooling time period after the firstheating time period based a previously determined amount of liquid orbased on stored heater activation data.

The electrically operated aerosol-generating system may be anelectrically operated vaping system.

According to some example embodiments, a method for determining anamount of liquid in an electrically operated aerosol-generating systemmay include: activating an electric heater for a first heating timeperiod in response to an input to vaporize liquid in a capillary wick,activating the electric heater for a second heating time period upon anelapse of a first cooling time period after the first heating timeperiod, recording a temperature measurement of the electric heaterduring or immediately following the second heating time period, anddetermining a liquid level in the liquid storage portion based on thetemperature measurement. The electrically operated aerosol-generatingsystem may include a liquid storage portion configured to store a liquidfrom which aerosol may be generated, an electric heater, a capillarywick between the liquid in the liquid storage portion and the electricheater and configured to convey liquid from the liquid storage portionto the electric heater, and electric circuitry connected to the electricheater, the electric circuitry configured to control activation of theelectric heater.

According to some example embodiments, a computer readable storagemedium has stored thereon a computer program which, when run onprogrammable electric circuitry in an electrically operatedaerosol-generating system, causes the programmable electric circuitry toperform the method. The electrically operated aerosol-generating systemmay include a liquid storage portion configured to store a liquid fromwhich aerosol may be generated, an electric heater, a capillary wickextending between the liquid storage portion and the electric heater andconfigured to convey liquid from the liquid storage portion to theelectric heater, and programmable electric circuitry connected to theelectric heater and configured to control activation of the electricheater.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be further described, by way of example only,with reference to the accompanying drawings, of which:

FIG. 1 shows one example of an electrically operated aerosol-generatingsystem having a liquid storage portion;

FIG. 2 is a plot showing five medians of temperature profiles of theheating element during multiple air draws of an electrically operatedaerosol-generating system;

FIG. 3 is an illustration of the wicking of liquid at low liquid level;

FIG. 4 is an illustration of the wicking of liquid from liquid held in acarrier material;

FIG. 5 is an illustration of activation of a heater in accordance withsome example embodiments; and

FIG. 6 is an illustration of activation of a heater in accordance withsome example embodiments.

DETAILED DESCRIPTION

Example embodiments will become more readily understood by reference tothe following detailed description of the accompanying drawings. Exampleembodiments may, however, be embodied in many different forms and shouldnot be construed as being limited to the example embodiments set forthherein. Rather, these example embodiments are provided so that thisdisclosure will be thorough and complete. Like reference numerals referto like elements throughout the specification.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises,” “comprising,”“includes,” and/or “including,” when used in this specification, specifythe presence of stated features, integers, steps, operations, and/orelements, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, and/or groupsthereof.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on”, “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, regions, layers and/orsections, these elements, regions, layers and/or sections should not belimited by these terms. These terms are only used to distinguish oneelement, region, layer or section from another region, layer or section.Thus, a first element, region, layer or section discussed below could betermed a second element, region, layer or section without departing fromthe teachings set forth herein.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper”, and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in operation in addition to the orientationdepicted in the figures. For example, if the device in the figures isturned over, elements described as “below” or “beneath” other elementsor features would then be oriented “above” the other elements orfeatures. Thus, the example term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Some example embodiments are described herein with reference tocross-section illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures). As such, variationsfrom the shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,these example embodiments should not be construed as limited to theparticular shapes of regions illustrated herein, but are to includedeviations in shapes that result, for example, from manufacturing. Forexample, an implanted region illustrated as a rectangle will, typically,have rounded or curved features and/or a gradient of implantconcentration at its edges rather than a binary change from implanted tonon-implanted region. Likewise, a buried region formed by implantationmay result in some implantation in the region between the buried regionand the surface through which the implantation takes place. Thus, theregions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the actual shape of a region of adevice and are not intended to limit the scope of this disclosure.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art. It will be further understood that terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and this specification and will not beinterpreted in an idealized or overly formal sense unless expressly sodefined herein.

Unless specifically stated otherwise, or as is apparent from thediscussion, terms such as “processing” or “computing” or “calculating”or “determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical, electronicquantities within the computer system's registers and memories intoother data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission or display devices.

As disclosed herein, the term “storage medium”, “computer readablestorage medium” or “non-transitory computer readable storage medium,”may represent one or more devices for storing data, including read onlymemory (ROM), random access memory (RAM), magnetic RAM, core memory,magnetic disk storage mediums, optical storage mediums, flash memorydevices and/or other tangible machine readable mediums for storinginformation. The term “computer-readable medium” may include, but is notlimited to, portable or fixed storage devices, optical storage devices,and various other mediums capable of storing, containing or carryinginstruction(s) and/or data.

Furthermore, at least some portions of example embodiments may beimplemented by hardware, software, firmware, middleware, microcode,hardware description languages, or any combination thereof. Whenimplemented in software, firmware, middleware or microcode, the programcode or code segments to perform the necessary tasks may be stored in amachine or computer readable medium such as a computer readable storagemedium. When implemented in software, processor(s), processingcircuit(s), or processing unit(s) may be programmed to perform thenecessary tasks, thereby being transformed into special purposeprocessor(s) or computer(s).

When the terms “about” or “substantially” are used in this specificationin connection with a numerical value, it is intended that the associatednumerical value include a tolerance of ±10% around the stated numericalvalue. Moreover, when reference is made to percentages in thisspecification, it is intended that those percentages are based onweight, i.e., weight percentages. The expression “up to” includesamounts of zero to the expressed upper limit and all valuestherebetween. When ranges are specified, the range includes all valuestherebetween such as increments of 0.1%. Moreover, when the words“generally” and “substantially” are used in connection with geometricshapes, it is intended that precision of the geometric shape is notrequired but that latitude for the shape is within the scope of thedisclosure. Although the tubular elements of the embodiments may becylindrical, other tubular cross-sectional forms are contemplated, suchas square, rectangular, oval, triangular and others.

In some example embodiments, an electrically operated aerosol-generatingsystem may include a liquid storage portion configured to store a liquidfrom which aerosol may be generated; an electric heater; a capillarywick positioned between the liquid in the liquid storage portion and theelectric heater (e.g., the capillary wick extends between the liquidstorage portion and the electric heater) and configured to convey liquidfrom the liquid storage portion to the electric heater; and electriccircuitry connected to the electric heater, the electric circuitryconfigured to: activate the electric heater for a vaporizing period(also referred to herein as a “first heating time period”) in responseto an input to vaporize liquid in the capillary wick, a first particular(or, alternatively, predetermined) time (also referred to herein as a“first cooling time period”) after the vaporizing period, activate theheater for a second period (also referred to herein as a “second heatingtime period”), record a temperature measurement of the heater during orimmediately following the second period, and determine a liquid level inthe liquid storage portion based on the temperature measurement.

During the vaporizing period, liquid in the wick is vaporized by theheat generated by the electric heater. This means that liquid from theliquid storage portion will be drawn into the capillary wick bycapillary action to replace the liquid that has been vaporized. The rateat which liquid is drawn into the wick is dependent on the level ofliquid in the liquid storage portion. If there is large amount of liquidin the liquid storage portion, the liquid will be drawn into the wick atfaster rate than if there is only a small amount of liquid remaining inthe liquid storage portion.

“Liquid level” as used herein refers to an amount of liquid in theliquid storage portion. It may be a percentage or proportion of amaximum amount of liquid or it may be an absolute amount of liquid. Theamount may be a mass or a volume of liquid, or a density of liquidwithin a carrier material.

As described, for a given amount of power applied to the electricheater, the rate of increase of heater temperature is dependent on theenvironment surrounding the heater and in particular on the amount ofliquid in the vicinity of the heater. When there is less liquid in thevicinity of the heating element, for a given amount of applied power theheating element will be heated to a higher temperature. So thetemperature measurement taken during the second period (“second heatingtime period”), or immediately after the second period, providesinformation about (“information associated with”) the amount of liquidin the wick and therefore the rate that liquid has been drawn into thewick following the vaporizing period. The temperature measurement is insome example embodiments made during the second period but may be madeimmediately after the second period. “Immediately after” in this contextmeans between 0 and 2 seconds after the second period. If thetemperature measurement is made after the second period, in some exampleembodiments it is made between 0 and 0.5 seconds after the secondperiod.

The electrically operated aerosol-generating system may be configured todeliver aerosol through an outlet portion. Air may be drawn into thesystem and through the outlet of the system, and generated aerosol maybe drawn out of the system through the outlet. Airflow as a result of auser a puff (also referred to herein as air being drawn through theoutlet) may be detected and used as a trigger to start the vaporizingperiod. The vaporizing period may also be ended at a time dependent on(“based on”) detected airflow through the system.

The first particular (or, alternatively, predetermined) time (e.g.,“first cooling time period”) is in some example embodiments shorter thana time needed for an amount of liquid in the wick to reach equilibriumfollowing the vaporizing period. This means that the temperaturemeasurement may be made as liquid is still wicking on to the capillarywick and the temperature measurement is directly related to the wickingrate of the liquid. Equilibrium in this context means a condition inwhich liquid is no longer being drawn into the wick because the wick issaturated or has reached hydrostatic equilibrium with the liquid withinthe liquid storage portion.

However, the time taken to reach equilibrium may be dependent on theliquid level within the liquid storage portion. It is possible for thefirst cooling time period to be greater than the time period associatedwith an amount of liquid in the wick reaching equilibrium following thevaporizing period during some conditions, such as when the liquidstorage portion is relatively full of liquid and to only be shorter thana period of time needed for an amount of liquid in the wick to reachequilibrium following the vaporizing period when the liquid storageportion is becoming empty.

In some example embodiments, the electric circuitry is configured toactivate the heater such that the temperature of the heater is lowerthan a vaporization temperature of the liquid during the second period(e.g., “second heating time period”). This means that the liquid leveldetermination can be made without vaporizing a significant amount ofliquid. This both reduces liquid consumption and reduces the possibilityof generated aerosol condensing within the system because it has notbeen drawn out of the system through the outlet thereof.

In some example embodiments, the step of activating the heater for asecond period is carried out only in absence of a further input duringthe first particular time (e.g., during the elapse of the first coolingtime period). In some example embodiments, the step of activating theheater for a second period comprises applying a particular (or,alternatively, predetermined) amount of electrical power to the heater.

By measuring heater temperature during a time period when air is notbeing drawn through the device and through an outlet thereof, a morereliable measurement can be obtained. The temperature of the heater maybe dependent not only on the amount of liquid in the vicinity of theheater but also on other factors, one of which may be airflow rate pastthe heater. Airflow past the heater as a result of air being drawnthrough the device and through an outlet thereof may have a coolingeffect on the heater. As airflow as a result of air being drawn throughthe device and through an outlet thereof is not consistent from drawingto drawing, this inevitably makes a determination of liquid level basedon temperature during air being drawn through the device and through anoutlet thereof less reliable. By measuring temperature at a time whenthe air is not being drawn through the device and through an outletthereof, the measurement is independent of airflow strength.

Most previous methods of determining liquid levels in systems of thistype have relied on measuring liquid consumption by monitoring heateractivation. Such previous methods may include determining an initialliquid level, and such determining may rely on storing heater activationdata over time. Some example embodiments do not require storage of anyheater activation data or knowledge of an initial liquid level. This isparticularly advantageous for systems in which the liquid storageportion is refillable to different levels (“amounts”) of liquid.

The electric circuitry may be configured to activate the heater for athird period (also referred to herein as a third heating time period) ata second particular (or, alternatively, predetermined) time after thesecond period (e.g., upon the elapse of a second cooling time periodafter the second heating time period), to record a temperaturemeasurement of the heater during the third period, and to determine aliquid level (e.g., amount of liquid) in the liquid storage portionbased on a combination of the temperature measurement of the heaterduring the third period and the temperature measurement of the heaterduring the second period. In particular, the liquid level in the liquidstorage portion may be based on a difference between the temperaturemeasurement of the heater during the third period and the temperaturemeasurement of the heater during the second period.

The temperature measurement of the heater during the third period andthe temperature measurement of the heater during the second period areindicative of the amount of liquid in the vicinity of the heater atthose times. A difference between those measurements therefore providesa measure of the wicking rate. This arrangement has the advantage thatit is independent of the level of liquid around the heater at the end ofthe vaporizing period. Although the amount of liquid remaining in thevicinity of the heater at the end of the vaporization period isgenerally quite consistent (and low), if the vaporizing period has beenvery short (because of a short or aborted draw of air, for example),there may be unusually high levels (“amounts”) of liquid remaining inthe wick in the vicinity of the heater.

In some example embodiments, the length of the vaporizing period (“firstheating time period”) or the total power applied during the vaporizingperiod (or some other parameter of the vaporizing period) may befactored into the determination of liquid level. It can be assumed thatthe longer the vaporizing period or the more power applied during thevaporizing period, the less liquid is in the vicinity of the heater atthe end of the vaporization period. This can be factored into acalculation of wicking rate based on a single temperature measurement.

In some example embodiments, the electric circuitry is configured toactivate the heater such that the temperature of the heater is lowerthan a vaporization temperature of the liquid during the third period.

In some example embodiments, the sum of the first particular (or,alternatively, predetermined) time (“first cooling time period”), thefirst period (“first heating time period”) and the second time (“secondcooling time period”) is shorter than a time needed for an amount ofliquid in the wick to reach equilibrium following the vaporizing period.This means that the temperature measurement is made as liquid is stillwicking on to the capillary wick when the heater temperature is measuredduring the third period (“third heating time period”).

The system may comprise one or more capillary wicks. The one or morecapillary wicks are configured to transfer liquid aerosol-formingsubstrate from the liquid storage portion to the heater. The one or morecapillary wicks may comprise a capillary material. A capillary materialis a material that is configured to actively convey liquid from one endof the material to another.

The structure of the capillary material may comprise a plurality ofsmall bores or tubes, through which the liquid can be transported bycapillary action. The capillary material may have a fibrous structure.The capillary material may have a spongy structure. The capillarymaterial may comprise a bundle of capillaries. The capillary materialmay comprise a plurality of fibers. The capillary material may comprisea plurality of threads. The capillary material may comprise fine boretubes. The fibers, threads or fine-bore tubes may be generally alignedto convey liquid to the aerosol-generating means. The capillary materialmay comprise a combination of fibers, threads and fine-bore tubes. Thecapillary material may comprise sponge-like material. The capillarymaterial may comprise foam-like material.

The capillary material may comprise any suitable material or combinationof materials. Examples of suitable materials are a sponge or foammaterial, ceramic- or graphite-based materials in the form of fibers orsintered powders, foamed metal or plastics materials, a fibrousmaterial, for example made of spun or extruded fibers, such as celluloseacetate, polyester, or bonded polyolefin, polyethylene, terylene orpolypropylene fibers, nylon fibers or ceramic. The capillary materialmay have any suitable capillarity and porosity so as to be used withdifferent liquid physical properties. The liquid aerosol-formingsubstrate has physical properties, including but not limited toviscosity, surface tension, density, thermal conductivity, boiling pointand atom pressure, which allow the liquid to be transported through thecapillary material by capillary action.

The one or more capillary wicks may have a first end and a second end.The first end may extend into the liquid storage portion and may beconfigured to draw liquid held in the liquid storage portion to theheater. The second end may extend into an air passage of theaerosol-generating system. The second end may comprise one or moreheating elements. The first end and the second end may extend into theliquid storage portion. The heater may comprise one or more heatingelements which may be arranged at a central portion of the wick betweenthe first and second ends. In use, when the one or more heating elementsare activated during the vaporization period (“first heating timeperiod”), the liquid in the one or more capillary wicks is vaporized atand around the one or more heating elements. The heating elements maycomprise a heating wire or filament. The heating wire or filament maysupport or encircle a portion of the one or more capillary wicks.

The liquid may have physical properties, including viscosity, whichallow the liquid to be transported through the one or more capillarywicks by capillary action.

The liquid may comprise nicotine. The nicotine containing liquid may bea nicotine salt matrix. The liquid may comprise plant-based material.The liquid may comprise tobacco. The liquid may comprise atobacco-containing material containing volatile tobacco flavorcompounds, which are released from the liquid upon heating. The liquidmay comprise homogenized tobacco material. The liquid may comprise anon-tobacco-containing material. The liquid may comprise homogenizedplant-based material.

The liquid may comprise at least one aerosol-former. An aerosol-formeris any suitable known compound or mixture of compounds that, in use,facilitates formation of a dense and stable aerosol and that issubstantially resistant to thermal degradation at the temperature ofoperation of the system. Suitable aerosol-formers are well known in theart and include, but are not limited to: polyhydric alcohols, such astriethylene glycol, 1,3-butanediol and glycerine; esters of polyhydricalcohols, such as glycerol mono-, di- or triacetate; and aliphaticesters of mono-, di- or polycarboxylic acids, such as dimethyldodecanedioate and dimethyl tetradecanedioate. Aerosol formers may bepolyhydric alcohols or mixtures thereof, such as triethylene glycol,1,3-butanediol and glycerine. The liquid aerosol-forming substrate maycomprise other additives and ingredients, such as flavorants.

The liquid may comprise water, solvents, ethanol, plant extracts andnatural or artificial flavors. The liquid may comprise nicotine and atleast one aerosol former. The aerosol former may be glycerine. Theaerosol-former may be propylene glycol. The aerosol former may compriseboth glycerine and propylene glycol. The liquid may have a nicotineconcentration of between about 0.5% and about 10%.

A carrier material may be arranged in the liquid storage portion forholding the liquid. The carrier material may be made from any suitableabsorbent body of material, for example, a foamed metal or plasticsmaterial, polypropylene, terylene, nylon fibers or ceramic. The liquidmay be retained in the carrier material prior to use of theaerosol-generating system. The liquid may be released into the carriermaterial during use. The liquid may be released into the carriermaterial immediately prior to use. For example, the liquid may beprovided in a capsule. The shell of the capsule may melt upon heating bythe heating means and releases the liquid aerosol-forming substrate intothe carrier material. The capsule may contain a solid in combinationwith the liquid.

The second period (“second heating time period”) may between 0.05 and0.5 seconds. It is only necessary to very briefly activate the heaterand measure the temperature before it approaches the vaporizationtemperature of the liquid.

The first particular (or, alternatively, predetermined) time period(“first cooling time period”) may be between 0.2 and 2 seconds. It isdesirable to provide a short time period of cooling of the heater beforereactivating it to ensure that the heater returns to a predicabletemperature and so that it remains below the vaporization temperature ofthe liquid during the subsequent activation of the heater. However, asexplained, it is also desirable to measure the temperature while liquidis being drawn onto the wick, i.e. before equilibrium is reached. Thetime period chosen for the first particular (or, alternatively,predetermined) time period will depend on the properties of thecapillary wick being used and on the properties of the liquid and theheater.

The electric circuitry may comprise a memory, wherein the memory storesa look-up table relating temperature measurements to liquid levels. Theelectric circuitry may be configured to compare measured temperatureswith stored temperature measurements to determine a liquid level. Therelationship between the measured temperature or temperature differenceand the liquid level in the liquid storage portion may be determinedempirically for a particular design of aerosol-generating system andstored in the memory as part of a manufacturing process.

The electric circuitry may comprise any suitable elements. The electriccircuitry may comprise a microprocessor. The microprocessor may be aprogrammable microprocessor.

The electric circuitry may be configured to control the supply of powerto the heater. The electric circuitry may be configured to supply aparticular (or, alternatively, predetermined) amount of power to theheater. The heater may be activated on supply of the particular (or,alternatively, predetermined) power by the electric circuitry. Theelectric circuitry may be configured to monitor the power supplied tothe aerosol-generating means.

The heater may comprise one or more heating elements. The one or moreheating elements may be arranged appropriately so as to most effectivelyheat the liquid in the capillary wick. The one or more heating elementsmay be arranged to heat the liquid primarily by means of conduction. Theone or more heating elements may be arranged substantially in directcontact with the liquid and wick. The one or more heating elements maybe arranged to transfer heat to the liquid via one or more heatconductive elements.

The one or more electric heating elements may comprise an electricallyresistive material. Suitable electrically resistive materials mayinclude: semiconductors such as doped ceramics, electrically“conductive” ceramics (such as, for example, molybdenum disilicide),carbon, graphite, metals, metal alloys and composite materials made of aceramic material and a metallic material.

The one or more electric heating elements may take any suitable form.For example, the one or more electric heating elements may take the formof one or more heating blades. The one or more electric heating elementsmay take the form of a casing or substrate having differentelectro-conductive portions, or one or more electrically resistivemetallic tube. The heater may comprise one or more heater filaments inthe form of a coil extending around the wick.

The heater may be a substantially flat heater. As used herein,“substantially flat” refers to a heater that is in the form of asubstantially two dimensional topological manifold. Thus, thesubstantially flat heater extends in two dimensions along a surfacesubstantially more than in a third dimension. In particular, thedimensions of the substantially heater in the two dimensions within thesurface is at least 5 times larger than in the third dimension, normalto the surface. An example of a substantially flat heater is a structurebetween two substantially parallel surfaces, wherein the distancebetween these two surfaces is substantially smaller than the extensionwithin the surfaces. In some embodiments, the substantially flat heateris planar. In other embodiments, the substantially flat heater is curvedalong one or more dimensions, for example forming a dome shape or bridgeshape.

The heater may comprise a plurality of heater filaments. The term“filament” is used throughout the specification to refer to anelectrical path arranged between two electrical contacts. A filament mayarbitrarily branch off and diverge into several paths or filaments,respectively, or may converge from several electrical paths into onepath. A filament may have a round, square, flat or any other form ofcross-section. A filament may be arranged in a straight or curvedmanner.

The plurality of filaments may be an array of filaments, for examplearranged parallel to each other. The filaments may form a mesh. The meshmay be woven or non-woven. The plurality of filaments may be positionedadjacent to or in contact with the capillary wick holding theaerosol-forming substrate. The filaments may define interstices betweenthe filaments and the interstices may have a width of between 10 μm and100 μm. The filaments may give rise to capillary action in theinterstices, so that in use, liquid to be vaporized is drawn into theinterstices, increasing the contact area between the heater assembly andthe liquid.

In one example, the heater comprises a mesh of filaments formed from304L stainless steel. The filaments have a diameter of around 16 μm. Themesh is connected to electrical contacts that are separated from eachother by a gap and are formed from a copper foil having a thickness ofaround 30 μm. The electrical contacts are provided on a polyimidesubstrate having a thickness of about 120 μm. The filaments forming themesh define interstices between the filaments. The interstices in thisexample have a width of around 37 μm, although larger or smallerinterstices may be used. Using a mesh of these approximate dimensionsallows a meniscus of aerosol-forming substrate to be formed in theinterstices, and for the mesh of the heater assembly to drawaerosol-forming substrate by capillary action. The heater is placed incontact with a capillary wick holding a liquid aerosol-formingsubstrate. The capillary material is held within a rigid housing and theheater extends across an opening in the housing.

The heating means (e.g., a heater) may comprise inductive heating means.For example, the heating means may include an inductive heater.

The electric circuitry may be arranged to measure the electricalresistance of the one or more electric heating elements. The electriccircuitry may be arranged to measure the electrical resistance of theone or more electric heating elements by measuring the current throughthe one or more electric heating elements and the voltage across the oneor more electric heating elements. The electric circuitry may beconfigured to determine the electrical resistance of the at least oneheating element from the measured current and voltage. The electriccircuitry may comprise a resistor, having a known resistance, in serieswith the at least one heating element and the electric circuitry may bearranged to measure the current through the at least one heating elementby measuring the voltage across the known-resistance resistor anddetermining the current through the at least one heating element fromthe measured voltage and the known resistance.

The electric circuitry may be configured to ascertain the temperature ofthe one or more electric heating elements from the measurements ofelectrical resistance. If the one or more heating elements have suitablecharacteristics, such as a suitable temperature coefficient ofresistance, the temperature of the one or more heating elements may beascertained from measurements of the electrical resistance of the one ormore heating elements.

The electrically operated aerosol-generating system may comprise twotemperatures sensors, a first temperature sensor and a secondtemperature sensor. The first temperature sensor may be the temperaturesensor arranged in the liquid storage portion for sensing thetemperature of liquid aerosol-forming substrate held in the liquidstorage portion. The second temperature sensor may being arranged tosense the temperature of the heater.

The electric circuitry may be configured to determine whether tosubsequently activate the heater for a second period, upon the elapse ofa first particular (or, alternatively, predetermined) time after thevaporizing period, based on a previously determined liquid level orbased on stored heater activation data. It may not be necessary ordesirable to subsequently activate the heater after every vaporizingperiod. For example, it may be desirable to determine liquid levelinfrequently when the most recent determination was that the liquidlevel is high, say over 50% of maximum capacity. It may be desirable todetermine liquid level more frequently as the determined liquid levelgets lower. It may be appropriate to determine liquid level only afterthe first vaporization period of each session of use of the system. Inthe case of a vaping system this means determining liquid level onlyafter the first draw of air.

Additional parameters may be factored into the determination of liquidlevel, including one or more of device orientation, liquid temperature,ambient temperature, type of liquid and type of heater and wickassembly. For example, the system may include one or more accelerometerto determine the orientation of the system. The orientation of thesystem may affect wicking rate and so may be factored into thedetermination of liquid level. The electric circuitry may be used withdifferent liquid storage portions and different heaters. The wickingrate may depend on the properties of the wick and of the liquid. Thetemperature of the heater for a given applied power may depend on thecharacteristics of the heater. The identity of the type of liquid andthe type of heater in the system may be used in the determination of theliquid level.

The electrically operated aerosol-generating system may further comprisean interface, wherein the electric circuitry is configured to indicatethe determined liquid level in the liquid storage portion through theinterface. The interface may be a display screen, one or more visualindicators, such as LEDs, an audio indicator such as speaker, a hapticindicator, or some combination of different indicators.

The liquid level may be indicated as an absolute amount of liquid, apercentage of a maximum liquid level, or as a determination that theliquid level is more or less than a threshold liquid level. The liquidlevel may be an average liquid level obtained from a plurality of liquidlevel determinations. The liquid level determined based on wicking ratemay be combined with other determinations of liquid level and withliquid consumption estimates or measurements, for example consumptionestimates based on heater activation time to provide a refined liquidlevel estimate.

The aerosol-generating system may comprise one or more electric powersupplies. The power supply may be a battery. The battery may be aLithium based battery, for example a Lithium-Cobalt, aLithium-Iron-Phosphate, a Lithium Titanate or a Lithium-Polymer battery.The battery may be a Nickel-metal hydride battery or a Nickel cadmiumbattery. The power supply may be another form of charge storage devicesuch as a capacitor. The power supply may require recharging and beconfigured for many cycles of charge and discharge. The power supply mayhave a capacity that allows for the storage of enough energy for one ormore generations of aerosol; for example, the power supply may havesufficient capacity to allow for the continuous generation of aerosolfor a period of around six minutes, or for a period that is a multipleof six minutes. In another example, the power supply may have sufficientcapacity to allow for a particular (or, alternatively, predetermined)number of draws of air through the system and the outlet thereof ordiscrete activations of the heating means and actuator.

The aerosol-generating system may comprise an input, such as a switch orbutton. This enables the system to be turned on. The switch or buttonmay activate the aerosol-generating means. The switch or button mayinitiate aerosol generation. The switch or button may prepare thecontrol electronics to await input from a detector.

The aerosol-generating system may comprise a housing. The housing may beelongate. The housing may comprise any suitable material or combinationof materials. Examples of suitable materials include metals, alloys,plastics or composite materials containing one or more of thosematerials, or thermoplastics that are suitable for food orpharmaceutical applications, for example polypropylene,polyetheretherketone (PEEK) and polyethylene. The material may be lightand non-brittle.

The housing may comprise a cavity configured to receive the powersupply. The housing may comprise a mouthpiece. The mouthpiece maycomprise at least one air inlet and at least one air outlet. Themouthpiece may comprise more than one air inlet. One or more of the airinlets may reduce the temperature of the aerosol before it is deliveredthrough the outlet of the system and may reduce the concentration of theaerosol before it is delivered through the outlet.

The aerosol-generating system may be portable. The aerosol-generatingsystem may have a total length between about 30 mm and about 150 mm. Theaerosol-generating system may have an external diameter between about 5mm and about 30 mm.

The aerosol-generating system may comprise a main unit and a cartridge.The main unit may comprise the electric circuitry. The cartridge maycomprise the liquid storage portion for holding the liquid. The mainunit may be configured to removably receive the cartridge.

The main unit may comprise one or more power supplies. The main unit maycomprise the heater. The cartridge may comprise the heater. Where thecartridge comprises the heater, the cartridge may be referred to as a‘cartomizer’.

The aerosol-generating system may comprise an aerosol-generating elementcomprising the heater. The aerosol-generating element may be separate tothe main unit and the cartridge. The aerosol-generating element may beremovably receivable by at least one of the main unit and the cartridge.

The cartridge may be removably coupled to the main unit. The cartridgemay be removed from the main unit when the liquid has been consumed. Thecartridge is in some example embodiments disposable. However, thecartridge may be reusable and the cartridge may be refillable withliquid. The cartridge may be replaceable in the main unit. The main unitmay be reusable.

As used herein, the term “removably received” is used to mean that thecartridge and the main unit can be coupled and uncoupled from oneanother without significantly damaging either the main unit or thecartridge.

In some example embodiments, there is provided a method for determininga liquid level of liquid in an electrically operated aerosol-generatingsystem, the electrically operated aerosol-generating system comprising aliquid storage portion storing a liquid from which aerosol may begenerated, an electric heater, a capillary wick positioned between theliquid in the liquid storage portion and the electric heater (e.g.,extending between the liquid storage portion and the electric heater)and configured to convey liquid from the liquid storage portion to theelectric heater, and electric circuitry connected to the electricheater, the electric circuitry configured to control activation of theelectric heater, comprising: activating the electric heater for avaporizing period in response to an input to vaporize liquid in thecapillary wick, a first particular (or, alternatively, predetermined)time after the vaporizing period, activating the heater for a secondperiod, recording a temperature measurement of the heater during orimmediately following the second period; and determining a liquid levelin the liquid storage portion based on the temperature measurement.

The method may further comprise activating the heater for a third periodat a second particular (or, alternatively, predetermined) time after thesecond period, recording a temperature measurement of the heater duringthe third period, and determining a liquid level in the liquid storageportion based on a combination of the temperature measurement of theheater during the third period and the temperature measurement of theheater during the second period. In particular, the liquid level in theliquid storage portion may be based on a difference between thetemperature measurement of the heater during the third period and thetemperature measurement of the heater during the second period.

In some example embodiments, there is provided a computer readablestorage medium having stored thereon a computer program which, when runon programmable electric circuitry in an electrically operatedaerosol-generating system, the electrically operated aerosol-generatingsystem comprising, a liquid storage portion storing a liquid from whichaerosol may be generated, an electric heater, a capillary wickpositioned between the liquid in the liquid storage portion and theelectric heater and configured to convey liquid from the liquid storageportion to the electric heater, and programmable electric circuitryconnected to the electric heater and configured to control activation ofthe electric heater, causes the programmable electric circuitry toperform the method according to some example embodiments.

It should be clear that some example embodiments can be implemented as asoftware update on existing hardware. In particular, it is possible toprovide a software update to existing aerosol-generating systems thatcomprise a programmable microprocessor for controlling the operation ofthe system and a data interface that allows for the uploading ofsoftware to the microprocessor.

Features of some example embodiments may be applied to some separateexample embodiments.

FIG. 1 shows one example of an electrically operated aerosol generatingsystem according to some example embodiments. Many other examples arepossible, however. FIG. 1 is schematic. In particular, the elementsshown are not to scale either individually or relative to one another.The aerosol generating system needs to include or receive anaerosol-forming substrate. The aerosol generating system requires aheater, for generating aerosol from the liquid and a wick or capillarymaterial for conveying the liquid to the heater. But other aspects ofthe system could be changed. For example, the overall shape and size ofthe housing could be altered.

In FIG. 1, the device has a liquid storage portion. The device 100 ofFIG. 1 comprises a housing 101 having an outlet end 103 and a body end105. In the body end, there is provided an electric power supply in theform of battery 107 and electric circuitry in the form of hardware 109and a detection device 111. In the outlet end, there is provided aliquid storage portion in the form of cartridge 113 containing liquid115, a capillary wick 117 and a heater 119 comprising at least oneheating element. Note that the heater is only shown schematically inFIG. 1. One end of the capillary wick 117 extends into the cartridge 113and the other end of the capillary wick 117 is surrounded by the heater119. Thus, the capillary wick 117 extends between the cartridge 113 andthe heater 119. The heater is connected to the electric circuitry viaconnections 121. The housing 101 also includes an air inlet 123, an airoutlet 125 at the outlet end and an aerosol-forming chamber 127.

The electric circuitry in the form of hardware 109 may include aprocessor and a memory. The memory may be a nonvolatile memory, such asa flash memory, a phase-change random access memory (PRAM), amagneto-resistive RAM (MRAM), a resistive RAM (ReRAM), or aferro-electric RAM (FRAM), or a volatile memory, such as a static RAM(SRAM), a dynamic RAM (DRAM), or a synchronous DRAM (SDRAM). Theprocessor may be, a central processing unit (CPU), a controller, or anapplication-specific integrated circuit (ASIC), that when, executinginstructions stored in the memory, configures the processor as a specialpurpose computer to perform the operations of the electric circuitry.Such operations performed by the electric circuitry may includecontrolling a supply of electrical power from a power supply of theaerosol-generating system to one or more of a pump of theaerosol-generating system and one or more elements (e.g., a heatingelement) of a vaporizer of the aerosol-generating system.

In use, operation is as follows. Liquid 115 is conveyed by capillaryaction from the liquid storage portion 113 from the end of the wick 117which extends into the liquid storage portion to the other end of thewick which is surrounded by heater 119. When air is drawn through theaerosol generating system and through the air outlet 125, ambient air isdrawn through air inlet 123. In the arrangement shown in FIG. 1, thedetection device 111 senses the draw of air and activates the heater119. The battery 107 supplies electrical energy to the heater 119 toheat the end of the wick 117 surrounded by the heater. The liquid inthat end of the wick 117 is vaporized by the heater 119 to create asupersaturated vapor.

The supersaturated vapor created is mixed with and carried in the airflow from the air inlet 123. In the aerosol-forming chamber 127, thevapor condenses to form an aerosol, which is carried towards the outlet125.

The liquid that has been vaporized is replaced by further liquid movingalong the wick 117 by capillary action.

The capillary wick can be made from a variety of porous or capillarymaterials and in some example embodiments has a known, pre-definedcapillarity. Examples include ceramic- or graphite-based materials inthe form of fibers or sintered powders. Wicks of different porositiescan be used to accommodate different liquid physical properties such asdensity, viscosity, surface tension and vapor pressure. The wick may besuitable so that a particular amount of liquid can be delivered to theheating element.

The heater in this example comprises a heating wire or filamentextending around the capillary wick. The temperature of heating elementmay be measured by measuring resistance of heater. The heating wire hasa temperature coefficient of resistance that allows for an accuratedetermination of the heater temperature to be made from a measurement ofelectrical resistance. The electric circuitry may comprise a resistor,having a known resistance, connected in series with the heating wire andthe electric circuitry may be arranged to measure the current throughthe at least one heating element by measuring the voltage across theknown-resistance resistor and determining the current through the atleast one heating element from the measured voltage and the knownresistance.

The rate of increase of temperature of the heating element when a givenamount of power is applied to the heater is dependent on the environmentsurrounding the heater, and in particular is dependent on the amount ofliquid in the vicinity of the heater. The more liquid there is aroundthe heating element the more heat will be lost to the liquid, which slowthe rate of temperature increase of the heating element. So, thetemperature of the heating element as the heating element is heating upis dependent on the amount on liquid in the wick, which is in turndependent on the wicking rate of the liquid at times before equilibriumhas been reached.

FIG. 2 is a plot showing five medians of temperature profiles beingmeasured during multiple air draws of an aerosol-generating system whenthe electric heater is activated because of a request for generatingaerosol. The temperature T of the heating element is shown on the y-axisand the air draw time t is shown on the x-axis. Curve 201 is the medianof a first set of air draws, each air draw having a 2-second air drawduration. Similarly, curve 203 is the median of a second set of airdraws, curve 205 is the median of a third set of air draws, curve 207 isthe median of a fourth set of air draws and curve 208 is the median of afifth set of air draws. In each curve, the vertical bars (for exampleshown at 209) indicate the standard deviation around the median forthose temperatures. Thus, the evolution of the measured temperature overthe life of the liquid storage portion is shown. This behavior wasobserved and confirmed for all liquid formulations vaporized and for allpower levels used.

As can be seen from FIG. 2, the temperature response of the heatingelement is reasonably stable over curves 201, 203 and 205. That is tosay, the standard deviation around the median for the first three setsof air draws is reasonably small. Over curve 207, two effects arenoticed. Firstly, the standard deviation around the median for the thirdset of air draws is greater. Secondly, the temperature of the heatingelement during each air draw has significantly increased. These twoeffects are the result of the liquid storage portion becoming empty sothat less liquid is delivered through the wick to the heater.

Over curve 208, the standard deviation around the median for the fifthset of air draws is smaller once again. That is to say, the temperaturerange over the air draws is reasonably stable. However, the temperatureof the heating element during each air draw has increased further. Thisis because the liquid storage portion is substantially empty.

The temperature increase in curve 207, as compared with curve 205, isparticularly evident after around 0.4 seconds of the air draw (shown bydotted line 211). Detecting differences in the amount of liquid in thevicinity of the heating element can therefore be accurately based on thetemperature level of the heating element after 0.4 seconds of the airdraw duration.

FIG. 2 demonstrates that there is a clear temperature increase of theheating element as the liquid storage portion becomes empty. This isparticularly evident after the first 0.4 seconds of an air draw. Thistemperature increase can be utilized to determine when the liquidstorage portion is empty or nearly empty.

It can also be seen in FIG. 2 that the slope of the temperature profilebetween 0 seconds and 0.2 seconds increases as the liquid storageportion becomes empty. Thus, a measure of the rate of temperatureincrease during an initial time of an air draw over the life of theliquid storage portion can provide an alternative or additional means todetect an amount of the remaining liquid in the liquid storage portion.

However, this technique can also be used to determine liquid level evenwhen the liquid storage portion is relatively full if measurement ismade while liquid is being drawn onto the wick following a vaporizingperiod (e.g., first heating time period). The rate of wicking of theliquid onto the wick is dependent on the liquid level in the liquidstorage portion. The rate of wicking can be determined by determiningthe amount of liquid on the wick at a first time, determining the amountof liquid on the wick a particular (or, alternatively, predetermined)time later (while the liquid is still wicking onto the coil), and thendividing the difference in the amounts of liquid by the particular (or,alternatively, predetermined) time. The amount of liquid in the wick isrelated to the temperature of the heating element early in a heateractivation, as described above. So by measuring the temperature of theheating element at different times as liquid is still being drawn ontothe wick, a measure of wicking rate can be obtained.

FIG. 3 illustrates one example of how liquid level in a liquid storageportion can affect the rate at which liquid is wicked to the heatingelement. The wick 300 in FIG. 3 is a bundle of fibers that, in effect,give rise to a plurality of capillary tubes through which liquid isdrawn. A heating element 310, in the form of a coiled filament, is woundaround one end of the wick 300. The opposite end of the wick extendsinto a liquid storage tank 320, which is half filled with liquid. FIG. 3illustrates the progress of liquid as it is drawn up the wick 300 to theheating element 310, with the initial state shown on the left and thefinal state (equilibrium) shown on the right. When the system is tilted,as shown in FIG. 3, the area of wick, and specifically the area of theend of the wick, in contact with the liquid is reduced. This reduces thewicking rate. The liquid transfers sideways across the wick into thatpart of the wick not in contact with the wick. This is a slower processthan wicking up the capillary tubes.

The lower the liquid level, the smaller the area of the end of the wickin contact with the wick and so the lower the wicking rate. Of coursethe system will not always be tilted at a one particular angle from thevertical, but nor will it remain perfectly vertical. It is also the casethat some liquid will be drawn into the wick through sidewalls of thewick. On average the lower the liquid level in the liquid tank the lowerthe wicking rate of liquid onto the wick.

FIG. 4 shows second example of how liquid level affects wicking rate.FIG. 4 illustrates a wick 400, a heating element 410 and a liquid tank420 as in FIG. 3. But in the example shown in FIG. 4 the liquid tank 420comprises a liquid carrier material 430. As the liquid in the liquidtank is consumed and the liquid level drops, the liquid is distributedacross the liquid carrier material and so the liquid density drops. Thismeans that as the liquid level drops the amount of liquid in contact incontact with the end of the wick is reduced. This reduces the wickingrate. FIG. 4a shows a relatively full liquid tank and FIG. 4b shows anemptier liquid tank, with a corresponding lower wicking rate up thewick.

Liquid level based on wicking rate can be determined in a number ofways. FIG. 5 illustrates a first embodiment of a control processconfigured to determine liquid level by determining wicking rate basedon a single heater activation. The process of FIG. 5 relies on anassumption that following a heater activation to vaporize liquid in thewick, the level of liquid in the vicinity of the wick is consistent. Soa measure of liquid level immediately after an activation of the heateris not measured but has been determined during a calibration processduring manufacture or device development.

FIG. 5 illustrates the activation of the heater over time. In FIG. 5power is applied to the heater in response to air being drawn throughthe system and through the outlet (referred to herein as an “air draw”and/or “draw of air”), as illustrated by vaporizing period 500. Theapplication of power to the heater in response to the air draw beingended at time t₀. At time t₀ the liquid in the wick is depleted as aresult of vaporization. At time t₁, which is a particular (or,alternatively, predetermined), constant period after to, power isapplied to the heater again for a second period 510. The second period510 is shorter than the vaporizing period 500 and is sufficiently shortthat the heater does not reach the vaporization temperature of theliquid during the second period. At time t₂, which is at or close to theend of the second period 510, the temperature of the heater is measured.The time t₂ is chosen to be a time at which liquid is still being drawnonto the wick, before equilibrium is reached, even when the liquidstorage portion is full. Because the liquid level in the wick at timet₀, and the temperature and cooling rate of the heater is assumed to beconsistent from air draw to air draw, the temperature of the heater attime t₂ is directly related to the wicking rate of liquid onto the wickand so is related to the liquid level in the liquid storage portion, asdescribed.

Empirical data for particular designs of aerosol-forming substrate andfor the particular system design can be stored in memory in the electriccircuitry. This empirical data can relate the temperature of the heatingelement at a t₂ with the amount of liquid remaining in the liquidstorage portion. The empirical data can then be used to determine howmuch liquid is remaining and may be used to provide an indication ofliquid level (“liquid amount”) or that liquid level is estimated to bebelow a threshold level.

FIG. 6 is a second embodiment of a control process configured todetermine liquid level based on two heater activations. In FIG. 6 poweris applied to the heater in response to air being drawn through thesystem and through the outlet thereof, as illustrated by vaporizingperiod 600. The application of power to the heater in response to thedraw of air being ended at time t₀. At time t₀ the liquid in the wick isdepleted as a result of vaporization. At time t₁, which is a set periodafter to, power is applied to the heater again for a second period 610.The second period 610 is shorter than the vaporizing period 600 and issufficiently short that the heater does not reach the vaporizationtemperature of the liquid. At time t₂, which is at or close to the endof the second period 610, the temperature of the heater is measured. Attime t₃, which is a set period after to, power is applied to the heateragain for a third period 620. The third period 620 is also shorter thanthe vaporizing period 600 and is sufficiently short that the heater doesnot reach the vaporization temperature of the liquid. At time t₄, whichis at or close to the end of the third period 620, the temperature ofthe heater is measured again. The time t₄ is chosen to be a time atwhich liquid is still being drawn onto the wick, before equilibrium isreached, even when the liquid storage portion is full.

The liquid level at the heater at time t₂ is determined from thetemperature measurement at time t₂. The liquid level at the heater attime t₄ is determined from the temperature measurement at time t₄. Thewicking rate is determined from the difference between the liquid levelat the heater at time t₂ and the liquid level at the heater at time t₄,divided by the time difference between t₂ and t₄. The determined wickingrate can be related to the liquid level in the liquid storage portionusing empirical data stored in a memory in the electric circuitry, asdescribed. An indication of liquid level can then be provided.

The determination of liquid level as described with reference to FIG. 5or FIG. 6 may be repeated after successive activations of the heater andan average liquid level may be determined and indicated. It is alsopossible to combine the described methods of liquid level estimationwith other techniques such as techniques that determine liquidconsumption based on a number or measurement of activations of theheater to provide a refined estimate of liquid level.

The estimation of liquid level may also be modified to account for othereffects, such as ambient temperature or liquid temperature, that mightaffect wicking rate, or the length of vaporizing period, that mightaffect the amount of liquid in the wick immediately following thevaporizing period.

Some example embodiments are applicable to different physicalarrangements of wick, heater and liquid storage portion. Empirical datacan be stored for each possible arrangement, and for different liquidsand adult vapors. For example, the wick may extend at both ends into theliquid storage portion with the heater at position intermediate the twoends. The heater, wick and liquid storage portion may also be providedin a cartridge or “cartomizer” separable from the electric circuitry.The electric circuitry may store empirical data relating to a pluralityof different cartridge or cartomizer designs that may store differentliquids.

Some example embodiments have a number of advantages. Measuring thewicking rate provides a means to estimate the liquid level withouthaving to continually monitor and store information about the systemusage. The methods of some example embodiments are therefore cheaper andsimpler to implement than prior methods that rely on continuallymonitoring heater usage.

some example embodiments may apply equally to cartomizers and tank basedsystems where the liquid storage portion can be refilled. some exampleembodiments may be used in systems where the starting liquid level isnot known.

Some example embodiments use automated activation of the heater thatdoes not rely on measurement during an activation. Automated activationcan be controlled more precisely than activation. The automatedactivation does not need to be implemented every time an adult vaporoperates the device. Power consumption can be greatly reduced byinfrequent use of the self-activation.

Some example embodiments may be implemented through modification tocontrol programs in existing systems. It may be possible simply toprovide software and data to existing systems in order to implement someexample embodiments.

The invention claimed is:
 1. An electrically operated aerosol-generatingsystem comprising: a liquid storage portion configured to store a liquidfrom which aerosol may be generated; an electric heater, the electricheater associated with a temperature coefficient of resistance; acapillary wick extending between the liquid storage portion and theelectric heater, the capillary wick configured to convey liquid from theliquid storage portion to the electric heater; an electric power supply;and electric circuitry connected to the electric heater, the electriccircuitry including a resistor electrically connected in series with theelectric heater, a processor, a memory, and a detection device, thedetection device configured to sense a draw of air through theelectrically operated aerosol-generating system, the processorconfigured to control a supply of electric power from the electric powersupply to the electric heater to controllably activate the electricheater, the resistor having a known electrical resistance, the memoryconfigured to store the temperature coefficient of resistance of theelectric heater, the known electrical resistance of the resistor, and anempirically-determined relationship between temperature differences ofthe electric heater and amounts of liquid in the liquid storage portion,wherein the processor is configured to activate the electric heater fora first heating time period, in response to air being drawn through theelectrically operated aerosol-generating system, such that liquid in thecapillary wick is vaporized during the first heating time period, andthe electric heater is deactivated at an ending of the first heatingtime period based on an end of the drawing of air through theelectrically operated aerosol-generating system, activate the electricheater for a second heating time period to supply a predetermined amountof power to the electric heater in response to an elapse of a firstcooling time period after the ending of the first heating time period,the second heating time period beginning at a first time and ending at asecond time such that the electric heater is deactivated at the secondtime, wherein the second heating time period is shorter than the firstheating time period and is sufficiently short such that a temperature ofthe electric heater remains below a vaporization temperature of theliquid and the liquid in the capillary wick is not vaporized during theactivation of the electric heater for the second heating time period,record a first temperature measurement of the electric heater at thesecond time at the ending of the second heating time period, such thatthe first temperature measurement is recorded while the temperature ofthe electric heater remains below the vaporization temperature of theliquid and the liquid is still wicking on to the capillary wick,activate the electric heater for a third heating time period to supplythe predetermined amount of power to the electric heater in response toan elapse of a second cooling time period after the ending of the secondheating time period, the third heating time period beginning at a thirdtime and ending at a fourth time such that the electric heater isdeactivated at the fourth time, wherein the third heating time period isshorter than the first heating time period and is sufficiently shortsuch that the temperature of the electric heater remains below thevaporization temperature of the liquid during the activation of theelectric heater for the third heating time period, record a secondtemperature measurement of the electric heater at the fourth time at theending of the third heating time period, such that the secondtemperature measurement is recorded while the temperature of theelectric heater remains below the vaporization temperature of the liquidand the liquid is still wicking on to the capillary wick, determine atemperature difference of the electric heater between the firsttemperature measurement of the electric heater and the secondtemperature measurement of the electric heater, and determine an amountof liquid in the liquid storage portion based an applying thetemperature difference of the electric heater to theempirically-determined relationship between temperature differences ofthe electric heater and amounts of liquid in the liquid storage portion,wherein the first and second temperature measurements of the electricheater are recorded, at the second and fourth times, respectively, basedon the processor measuring a voltage across the electric heater, theprocessor measuring a voltage across the resistor that is electricallyconnected in series with the electric heater, the processor determiningan electrical current through the electric heater based on the knownelectrical resistance of the resistor and the voltage across theresistor and further based on the resistor being electrically connectedin series with the electric heater, the processor determining anelectrical resistance of the electric heater based on the voltage acrossthe electric heater and the electrical current through the electricheater, and the processor determining a temperature of the electricheater based on the electrical resistance of the electric heater and thetemperature coefficient of resistance of the electric heater.
 2. Theelectrically operated aerosol-generating system according to claim 1,wherein the capillary wick has a fibrous or spongy structure.
 3. Theelectrically operated aerosol-generating system according to claim 1,wherein the liquid storage portion is configured to retain the liquid ina liquid carrier material.
 4. The electrically operatedaerosol-generating system according to claim 1 wherein the secondheating time period is between 0.05 and 0.5 seconds.
 5. The electricallyoperated aerosol-generating system according to claim 1, wherein theelapse of the first cooling time period is between 0.2 and 2 secondsafter the ending of the first heating time period.
 6. The electricallyoperated aerosol-generating system according to claim 1, wherein theelectric circuitry is configured to determine whether to subsequentlyactivate the electric heater for the second heating time period upon theelapse of the first cooling time period after the first heating timeperiod based on a previously determined amount of liquid or based onstored heater activation data.
 7. The electrically operatedaerosol-generating system according to claim 1 wherein the electricallyoperated aerosol-generating system is an electrically operated vapingsystem.
 8. A method for determining an amount of liquid in anelectrically operated aerosol-generating system, the electricallyoperated aerosol-generating system including a liquid storage portionconfigured to store a liquid from which aerosol may be generated, anelectric heater, a capillary wick between the liquid in the liquidstorage portion and the electric heater and configured to convey liquidfrom the liquid storage portion to the electric heater, and electriccircuitry connected to the electric heater, the electric circuitryconfigured to control activation of the electric heater, the methodcomprising: activating the electric heater for a first heating timeperiod in response to air being drawn through the electrically operatedaerosol-generating system, such that liquid in the capillary wick isvaporized during the first heating time period, and the electric heateris deactivated at an ending of the first heating time period based on anend of the drawing of air through the electrically operatedaerosol-generating system, activating the electric heater for a secondheating time period in response to an elapse of a first cooling timeperiod after the ending of the first heating time period, the secondheating time period beginning at a first time and ending at a secondtime such that the electric heater is deactivated at the second time,wherein the second heating time period is shorter than the first heatingtime period such that a temperature of the electric heater remains belowa vaporization temperature of the liquid and the liquid in the capillarywick is not vaporized during the activation of the electric heater forthe second heating time period, recording a first temperaturemeasurement of the electric heater at the second time at the ending ofthe second heating time period, such that the first temperaturemeasurement is recorded while the temperature of the electric heaterremains below the vaporization temperature of the liquid and the liquidis still wicking on to the capillary wick; activating the electricheater for a third heating time period in response to an elapse of asecond cooling time period after the ending of the second heating timeperiod, the third heating time period beginning at a third time andending at a fourth time such that the electric heater is deactivated atthe fourth time, wherein the third heating time period is shorter thanthe first heating time period such that the temperature of the electricheater remains below the vaporization temperature of the liquid duringthe activation of the electric heater for the third heating time period,recording a second temperature measurement of the electric heater at thefourth time at the ending of the third heating time period, such thatthe second temperature measurement is recorded while the temperature ofthe electric heater remains below the vaporization temperature of theliquid and the liquid is still wicking on to the capillary wick,determining a temperature difference between the first temperaturemeasurement and the second temperature measurement, and determining anamount of liquid in the liquid storage portion based on applying thetemperature difference to an empirically-determined relationship, storedin a memory of the electric circuitry, between temperature differencesand amounts of liquid in the liquid storage portion.
 9. The methodaccording to claim 8, wherein the second heating time period is between0.05 and 0.5 seconds.
 10. The method according to claim 8, wherein theelapse of the first cooling time period is between 0.2 and 2 secondsafter the ending of the first heating time period.
 11. The methodaccording to claim 8, further comprising: determining whether tosubsequently activate the electric heater for the second heating timeperiod upon the elapse of the first cooling time period after the firstheating time period based on a previously determined amount of liquid orbased on stored heater activation data.